You're probably applying more pressure than you realize to tighten a used crush washer and subsequently fatiguing the aluminum bolt over time. A crush washer keeps things sealed by friction and not torque.You are correct, they are single use only. That said, I have re-used a crush washer before when rebuilding my fork and noticed little difference. A tiny bit more weeping, but not enough to make a tangible difference before the next service interval.
I'm kind of in the same boat. My fork needs a damper rebuild but I don't want to do it until I get my hands on a bag of crush washers.